1. Field of the Invention
Aspects of the present invention generally relate to apparatus and methods for handling wellbore fluids from a well. Specifically, the aspects of the present invention relate to apparatus and methods of recycling wellbore fluids during underbalanced drilling. The aspects of the present invention further relates to apparatus and methods of handling wellbore fluids during well testing.
2. Description of the Related Art
In conventional drilling of wellbores for the production of hydrocarbons, drilling mud is generally used as the circulating medium. The drilling mud is typically made up of a fluid mixture of water and a suitable additive. The drilling mud is injected under pressure through a tubing to the bottom of the wellbore. During operation, the drilling mud at the bottom is continuously circulated to the surface. One of the functions of the drilling fluid is to carry and remove any rock cuttings resulting from the drilling operation to the surface. Another function is to exert a hydrostatic pressure at the bottom of the wellbore to prevent hydrocarbons in the formation from entering the wellbore.
Because the hydrostatic pressure in the wellbore is greater than the formation pressure, the drilling mud will most likely penetrate into or invade the formations surrounding the wellbore. Drilling mud that has penetrated into the formation reduces the permeability of the wellbore, thereby impeding the flow of hydrocarbons into the wellbore. As a result, the productivity of the well can be adversely affected. This type of wellbore damage is generally known as “skin damage” and may extend from a few centimeters to several meters from the wellbore.
More recently, underbalanced drilling was developed to overcome this problem. Underbalanced drilling involves maintaining the equivalent circulating or hydrostatic pressure of the fluid in the wellbore below the formation pressure. This underbalanced condition may be achieved by using a “lightened” drilling fluid as the circulating medium. Examples of lightened drilling fluid include fluids mixed with a gas, such as air, nitrogen, or natural gas. The gas may be introduced at the surface into the drill string for delivery at the bottom of the wellbore. The lightened drilling fluid exerts a hydrostatic pressure at the bottom of the wellbore that is below the formation pressure. In this manner, the underbalanced condition may be maintained.
Drilling fluid returning to the surface typically contains the cuttings from the drilling. Because the underbalanced state may allow a net flow of gas or oil into the wellbore, the return fluid may also contain liquid and gaseous hydrocarbons mixed with the circulating mud when the well penetrates a formation containing hydrocarbons. Therefore, the return fluid reaching the surface may be made up of four phases: solids (cuttings), water, oil, and gas.
The return fluids are typically conveyed into a closed pressure vessel separator. In the separator, the return fluids are separated and delivered into separate streams. In most cases, the separated gas stream is delivered to a flare line or a vent line. When the separated gas stream contains nitrogen or hydrocarbons, valuable resources are unnecessarily wasted or destroyed. Moreover, the separated gas stream is typically disposed in an environmentally unfriendly manner such as flaring.
Therefore, there is a need for a method of recycling the separated gas stream to avoid unnecessary waste. There is also a need for an apparatus for handling multiphase return fluids and recycling the gas stream. There is a further need for an apparatus for handling multiphase return fluids with reduced flaring of the gas stream.